The proposed research is an extension of ongoing studies on the growth and development of the sympathetic and sensory nervous systems. Using immunocytochemical, biochemical and pharmacologic techniques we have found that bidirectional interactions across the synapse regulate development, and have begun to define these trans-synaptic molecular messages and their trophic effects in the neonate. In parallel studies in the embryo we have begun to define the factors governing phenotypic expression in neuroblasts, the factors regulating embryogenesis and the role of nerve growth factor in the regulation of sympathetic and sensory development. The present studies will focus on the molecular mechanism regulating nerve growth in the sympathetic and sensory nervous systems. More specifically we hope to (a) define the mechanisms by which the central nervous system regulated maturation of neurotransmitter enzymes in sympathetic neurons; (b) further characterize the trans-synaptic messages in sympathetic ganglia; (c) characterize the role of nerve growth factor in sympathetic and sensory embryogenesis; (d) define the factors which regulate initial phenotypic expression in embryonic neuroblasts; (e) determine whether neuroblasts normally change transmitter phenotype in the embryo; (f) use the above information to understand inter-neuronal communication and synaptic plasticity. @DTX* 1NB-3192-22*